Method of manufacturing monodisperse poly (meth) acrylate particles

ABSTRACT

The invention relates to a method of manufacturing monodisperse poly(meth)acrylates by the method of precipitation polymerization, comprising polymerizing 
     i) a monomer mixture comprising at least 60 wt. % of monomer of formula I ##STR1##  where R represents hydrogen or methyl; and 
     R 1  represents a C 1-8  alkyl group, a C 6-24  aryl group, a C 1-8  alkyl substituted aryl group or an aralkyl group; 
     ii) 0.1-10 wt. % based on the weight of the monomer mixture of a block copolymer having polystyrene components; and 
     iii) 0.02-2 wt. % based on the weight of the monomer mixture of a percarbonic acid ester; 
     in a halogen free solvent comprising 70 to 100 wt. % of cyclohexane.

This is a Division of application Ser. No. 08/288,032, filed on Aug. 10,1994.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method of manufacturing monodispersepoly(meth)acrylate particles of stable shape, having diameter 1-20micron.

2. Discussion of Related Art

The evidence in the industry indicates a growing demand for plastics inthe form of elastic particles of stable shape having a defined, uniformparticle size in the range 2-20 micron. Such particles are used, e.g.,as spacers (e.g. in displays and films), surface modifying agents,support materials in diagnostics, etc.

However, the primary interest is in the area of the optics industry, inwhich particles in this size range having an index of refraction whichcan be precisely adjusted with respect to the index of refraction of agiven polymer matrix can be used to achieve various optical effects.

In this connection, the profile of required properties for suchparticles with diameter 5-15 micron has long been known; however, therehas not been available a practicable method of manufacturing suchparticles. The classical method of manufacturing defined particles,emulsion polymerization, does not succeed in this particle range (see1992, "Ullmanns Encyclopedia of Industrial Chemistry"., 5th Ed., Vol.A21, pub. VCH, pp. 168, 373-387; Becker and Braun, 1990,"Kunststoff-Handbuch", Vol. 1, pub. Carl Hanser, pp. 26-28). In general,emulsion polymerization can be used to produce particles with diameter≦2 micron, but attempts to produce larger particles are accompanied byproblems, in particular formation of new particles, leading tomultimodal particle size distributions. According to literature data itshould be possible to manufacture particles of the stated size byrepetitive absorption of aqueous dispersions containing monomers (seeUgelstad, J., Mork, P. C., Kaggurud. K. H., Ellingsen, T. and Berge, A.,1980 Adv. Colloid Interface Sci. 13, 191).

However, the method described is very complex. Another method, whereinthe subject particles are manufactured in an environment withmicrogravity (in a space shuttle in space), holds little promise forindustrial exploitation (see Vanderhoff, J. W., El-Asser., M. S.,Micale, F. J. 1, Sudol., E. D., Tsena, C. M., Silwanowicz, A., Sheu, H.R., and Kornfeld. D. M., 1986 P-Mater. Sci. Eng. Prepr. 54, 587). Thusit is concluded that heretofore no simple, industrially applicablemethod existed for manufacturing such particles in water as the reactionmedium. Also, classical suspension polymerization technique, wherein itis well known that particle size is controlled primarily by the stirringspeed, generally does not yield particles in the size range 5-15 micron.Moreover, these particles are not monodisperse, but have a wide particlesize distribution.

The principal applications of these particles are light scatteringapplications wherein the index of refraction of the particles is animportant factor (see Jap. Pat. App. 03-126,766; Chem. Abstr. 115,209446n). Particles having a core-and-shell structure in this size rangeare frequently used for, e.g., matt coatings (Jap. Pat. App. 03-58,840;Chem. Abstr. 115, 116478; Eur. OS 342,283).

The possibility is more favorable of obtaining monodisperse PMMAparticles with diameter 2-20 micron by producing the particles by theprinciple of precipitation polymerization in an organic medium, with theuse of an organic dispersant.

There have been a relatively large number of publications on thissubject. Precipitation polymerization of PMMA in hydrocarbons assolvents was proposed as early as the 1930s (U.S. Pat. No. 2,135,443,Ger. Pat. 662,157). Since then over 100 patent-type publications andnumerous other publications have appeared which deal with polymerizationof alkyl(meth)acrylates in non-aqueous dispersions.

In many of the patent-type publications mentioned, the applicationsdescribed relate purely to paints and similar coatings, involving stableorganic dispersions of very fine particles. There are also publicationsreporting investigation of the effect of emulsifiers, initiators, andsolvent grade on the particle size. A very informative summary ofdispersion polymerization of methyl methacrylate in non-aqueous media isprovided in Winnik, M. A., et al., 1987, Makromol. Chem. Macromo. Symp.10/11, 483-501.

Block copolymers are the most prominent emulsifiers used for dispersionpolymerization. An overview of currently used polymerization conditionsis provided in Winnik, M. A., et al., loc.cit., p. 485 (Table 1).

It may also be seen from Winnik, M. A., et al., loc.cit,, that theparticle size is controllable via the emulsifier concentration (FIG. 1),the initiator concentration (FIG. 5), and the solids content (FIG. 3)and solvent grade (FIG. 4). The graphics presented therein indicate thatit is particularly possible to control in favor of larger particles (>3micron) with the use of mixtures of tetrachloromethane and alkanes. Ifhalogenated hydrocarbons are not employed, regimes are encountered inwhich it is not possible to control particle size; instead, coagulationoccurs.

The use of halogenated hydrocarbons in industry can no longer bejustified, because of deleterious ecological and toxicological effects.Accordingly, there is a need as described above, for means of producingmonodisperse poly(meth)acrylate particles, preferably in the range ofparticle sizes of 1-20 micron, without the use of objectionablesubstances such as halogenated hydrocarbons. This problem is solved bythe inventive method, which prescribes a specific formulation.

SUMMARY OF THE INVENTION

Accordingly, one object of the invention is to provide a method ofmanufacturing monodisperse poly(meth)acrylates by the method ofprecipitation polymerization, comprising polymerizing

i) a monomer mixture comprising at least 60 wt. % of monomer of formulaI ##STR2## where R represents hydrogen or methyl; and R₁ represents aC₁₋₈ alkyl group, a C₆₋₂₄ aryl group, a C₁₋₈ alkyl substituted arylgroup, particularly phenyl, or an aralkyl group, particularly benzyl;

ii) 0.1-10 wt. % based on the weight of the monomer mixture of a blockcopolymer having polystyrene components; and

iii) 0.02-2 wt. % based on the weight of the monomer mixture of apercarbonic acid ester;

in a halogen free solvent comprising 70 to 100 wt. % of cyclohexane.

The inventively produced poly(meth)acrylate particles have particlesizes which, as a rule lie completely within the range 1-20 micron,preferably 2-20 microns (with the convention that the diameter in theplane of greatest extent is the measure of the particle size). (Particlesizes are determined with a light microscope.)

In contrast to classically manufactured polymer beads, the products ofthe inventive method have a very narrow size distribution; accordingly,in the context of the present invention they are described as"monodisperse". This is understood to signify that at least 80 wt. % ofthe particles, preferably 90 wt. % lie within a size range of ±20% fromthe stated mean value. On occasion, relatively small proportions (<5 wt.%) of finer particles may be produced; these are not deleterious to theapplications envisioned.

BRIEF DESCRIPTION OF THE DRAWINGS

Various other objects, features and attendant advantages of the presentinvention will be more fully appreciated as the same becomes betterunderstood from the following detailed description when considered inconnection with the accompanying drawings in which like referencecharacters designate like or corresponding parts throughout the severalviews and wherein:

FIG. 1 shows the particles at a magnification of ˜1:1000.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The solvents employed according to the invention are halogen-free.Accordingly the solvent is not substituted with halogen groups.

The block copolymers with polystyrene components are preferably selectedfrom the group comprised of a polystyrene with an ethylene-co-propyleneblock (hydrogenated polyisoprene); and a polystyrene with anethylene-co-butylene block (hydrogenated polybutadiene).

The amount of the polystyrene block with respect to the amount of theother block copolymer component in the block copolymer is preferably inthe range of 20-50 wt. %.

In general, the block copolymer has a molecular weight in the rangeM_(w) =30,000-200,000, preferably 70,000-130,000.

The primary candidate for the monomer of formula I is methylmethacrylate, preferably comprising at least 20 wt. % of the monomermixture and possibly as much as 100 wt. %. The other monomers (if any)may be, particularly, methyl acrylate, ethyl(meth)acrylate, butylacrylate, isobutyl methacrylate, and/or 2-ethylhexyl(meth)acrylate, inamounts up to 20 wt. % each.

In general among the monomers of formula I those in which R representsCH₃ (i.e. methacrylates) are preferred.

To increase the index of refraction, preferably C₆₋₁₄ aryl- and/or C₆₋₁₄aralkyl(meth)acrylates are used, particularly phenyl-, tolyl-,naphthyl-, benzyl-, and,/or phenylethyl(meth)acrylate(s), in amounts of1-80 wt. %., preferably from 10-60 wt. %, more preferably from 30-40 wt.%. based on the total weight of the monomer mixture. Advantageously theamount of vinylaromatics, such as styrene and its homologs, is limitedto <20 wt. % (based on the weight of monomer mixture), because thesemonomers substantially disturb the course of the polymerization.

The particle size can be regulated in favor of reduced size by the useof hydrophilic monomers. Candidates for use as hydrophilic monomers are,e.g., hydroxy- and/or (possibly) alkyl-substituted C₁₋₁₂ aminoalkylesters of (meth)acrylic acid, and the corresponding amides.

Hydrophobic comonomers such as, e.g., the above-mentioned isobutylmethacrylate, phenyl methacrylate, and/or benzyl methacrylate, which maybe employed in the amount of 0-C. 70 wt. % (based on the weight of themonomer mixture), regulate the particle size in favor of increased size.

Crosslinking of the monomers may be provided for by employing graftingcrosslinkers, i.e. monomers having two radically polymerizable groups ofdifferent reactivity, e.g. allyl(meth)acrylate, in amounts of 0.1-20 wt.% (based on the total weight of the monomer mixture). On the other hand,as to crosslinking monomers having identical or similar polymerizablegroups, e.g. (meth)acrylate esters of polyhydric alcohols, one shouldlimit their use to <1 wt. % (based on the total weight of the monomermixture).

The solvent, or solvent mixture, may contain ≦30 wt. % of othersolvents, but not halogenated solvents, e.g. polar solvents such asbutyl acetate.

The percarbonic acid esters proposed as initiators according to theinvention are known. Candidates for use as this component are, e.g., inparticular, bis(4-tert-butylcyclohexyl)-peroxydicarbonate anddicyclohexylperoxydicarbonate (obtainable from the firm Peroxidchemie,under the trade name Interox BCHPC® or Interox CHPC®). (See Brandrup andImmergut, 1989, "Polymer Handbook". 3rd Ed., pub. J. Wiley, p. II-1.)

The amount of percarbonic acid ester initiator used is from 0.02-2 wt.%, preferably from 0.1-1 wt. %, more preferably from 0.2-0.5 wt. % basedon the total weight of the monomer mixture.

The styrene block copolymers preferably are comprised of polystyreneblocks in the amount of 30-50 wt. %, in addition to propylene- and/orbutylene blocks derived from hydrogenation of polyisoprene and/orpolybutadiene; for example a styrene-isoprene block copolymer of thetype of SHELLVIS 50® (available from Shell).

The amount of styrene block copolymer used is from 0.1 to 10 wt. %,preferably from 0.2-5 wt. %, more preferably from 0.5-1 wt. % based onthe total weight of the monomer mixture.

The polymerization may be carried out in a reactor suitable forprecipitation polymerization with small reaction volumes, e.g. a 500 mlthree-neck flask equipped with a condenser, a device for supplying aninert gas, a thermometer, and a stirrer. Advantageously the method iscarried out under an inert gas such as argon or nitrogen.Advantageously, one initially charges the following to the reactor toform a solution: the solvent, the monomer mixture (particularly themonomer of formula I), and the emulsifier. A suggested amount of thesolvent is, e.g., 150 parts by weight (pbw) (based on the weight of themonomer mixture). Preferably, pure cyclohexane is used. Then thereaction mixture is heated, e.g. to 60° C. When the selected interiortemperature is reached, the polymerization is initiated under stirringby adding the initiator, preferably dissolved in a small amount ofcyclohexane.

Ordinarily the temperature rises automatically after a short time, e.g.1 min, wherein the previously clear solution becomes cloudy. After c. 5min, in general the reaction mixture has already turned white. Under theconditions reported, after 20 min the internal temperature is likely tohave reached 81° C., at which point said temperature may remain at thislevel for several minutes, as a result of cooling caused by boiling.

In a typical precipitation polymerization, the process advances quiterapidly, so that attention must be paid to adequate cooling andstirring. For after-reaction, one maintains the mixture at c. 80° C. fora certain time further, e.g. c. 1 hr, under stirring, and then cools itto room temperature, also under stirring.

The dispersions obtained in this manner are almost completely free ofcoagulates. Monodisperse polymer particles in the prescribed particlesize range (diameter 1-20 micron) are obtained.

The method may be used to produce pure polymethacrylate particles oruncrosslinked copolymer particles, or, preferably, crosslinkedparticles, where allyl methacrylate is preferred as a crosslinkingagent.

Of interest are crosslinked, homogeneous particles comprised of MMA inthe amount of 90-99.5 wt. % and allyl methacrylate in the amount of10-0.5 wt. %, in the particle size range 4.0-10.0 μm.

Also preferred are crosslinked particles comprised of allyl methacrylate(0.5-10 wt. %), phenyl methacrylate (10-50 wt. %), and methylmethacrylate (40-89.5 wt. %), as well as additional methacrylate esters(0-20 wt. %).

Of particular interest are crosslinked particles of the followingcomposition:

30-80 wt. % methyl methacrylate

60-19.5 wt. % benzyl methacrylate

10-0.5 wt. % allyl methacrylate,

with particle size 4-12 micron, preferably 5-11 micron, particularlypreferably 7.5±2 micron.

The particularly preferred content of allyl methacrylate is in the range3-7 wt. %, more particularly 4-6 wt. %. The benzyl methacrylate may bepartially or completely replaced by phenylpropyl methacrylate orphenylethyl methacrylate. Also, the methyl methacrylate may be replacedin amounts of up to c. 10 wt. % by other (meth)acrylic acid esters, e.g.isobutyl methacrylate.

Particles with a smooth surface are of interest. However, from thestandpoint of application technology, particles having a rough surfaceare particularly valuable.

Particularly preferred are round, crosslinked particles with a roughsurface, in a particle size range of 5.5-9.5 micron, having thefollowing approximate composition:

55 wt. % methyl methacrylate

40 wt. % benzyl methacrylate

5 wt. % allyl methacrylate.

Particularly preferred are particles of this type in which theabove-prescribed copolymer composition comprising methyl methacrylate,benzyl methacrylate, and allyl methacrylate is relatively homogeneousthroughout the particle--thus, particles which do not have acore-and-shell structure. Such particles, having a rough surface, and aparticle size range of 4-12 micron, particularly 7.5±2 micron, with theabove-mentioned polymer composition comprising methyl methacrylate,benzyl methacrylate, and allyl methacrylate, are highly suitable forincorporating in molding compounds.

In general, the described method is especially well suited formanufacturing particles with an index of refraction of 1.48-1.58 and aparticle size in the range 4-12 micron.

Preferred are particles with an index of refraction n_(D) ²⁰ in therange 1,500-1.550, preferably 1.510-1.530, and a particle size of 7.5±2micron.

Particularly preferred are, as described above, particles of acomposition comprising methyl methacrylate, benzyl methacrylate, andallyl methacrylate, having a rough surface, with the structure of thesurface roughness of the particle being such that it is clearlyrecognizable under a light microscope at a magnification of c. 500×.

Such particles, particularly such particles with a rough surface andhaving a particle diameter of 4-12 micron, preferably 7.5±2 micron, areespecially well suited for incorporating in molding compounds, inamounts of 0.01-60 wt. %, preferably 0.5-25 wt. %.

All thermoplastically processible molding compounds are possibilitiesfor incorporating such particles, particularly molding compounds whichare amorphous, highly transparent, and possibly colored, which moldingcompounds are of the type of polymethacrylate, polymethacrylate-styrenecopolymers, polymethacrylate-styrene-maleic anhydride copolymers,polymethacrylimides, polycarbonates (particularly bisphenol-Apolycarbonate), polystyrene, and polyvinyl chloride. Of particularinterest are molding compounds based on polymethyl methacrylate andpolycarbonate.

The molding compounds can be used as such or with impact strengthmodifiers.

In addition to the use of the inventive particles in molding compounds,they may be used in casting resins. They may be particularly used, aswell, by incorporating them in paints and the like, particularly inreactive paints which are UV-curable, in amounts of 0.01-30 wt. %.

When the monodisperse particles are used in molding compounds, they maybe employed in concentrates (master batches) or in direct dry mixtures.Molding compounds or dry mixtures containing these particles may beprocessed by known thermoplastic methods, e.g. extruding, injectionmolding, injection blow-molding, extrusion blowing, and extrusion.

The monodisperse polymer beads can be used advantageously for puresurface upgrading of molded articles; or special optical effects can beachieved by incorporating these particles in molding compounds,coextrusion compounds, or paints and the like.

Molding compounds containing these monodisperse particles may beused,.particularly, in manufacturing rear-projection screens, TV screens(e.g. diaprojection screens or image devices in general), projectionscreens, protective covers or masks for monitors, scale covers (onmeasuring instruments), lamp covers, and dispersion lenses.

Room divider walls may also be manufactured with molding compoundscontaining the inventive beads.

The applications mentioned represent only a small fraction of thepotential applications for molding compounds containing thesemonodisperse particles, particularly such particles having roughsurfaces.

The following Examples serve to illustrate the invention. In theExamples, the particle sizes were determined by a light microscope.

Having generally described this invention, a further understanding canbe obtained by reference to certain specific examples which are providedherein for purposes of illustration only and are not intended to belimiting unless otherwise specified.

EXAMPLE 1

The following compounds were dissolved in a 500 mL three-neck flaskequipped with a condenser, an argon feed, a thermometer, and a stirrer,and were heated to 60° C.:

150 g cyclohexane

100 g methyl methacrylate

0.625 g hydrogenated styrene-isoprene block copolymer, comprised of 40pbw styrene and 60 pbw isoprene. Nonuniformity U=0.04. (The productSHELLVIS 50®, supplied by Shell Intl. Chemical Co., London.)

When the internal temperature had reached 60° C., the polymerization wasinitiated by addition of 1 gbis(4-tert-butylcyclohexyl)-peroxydicarbonate (dissolved in a smallamount of cyclohexane). Within 1 min the temperature rose to 61° C. Thepreviously clear solution became appreciably cloudy. Within 5 min thereaction mixture was white. After 20 min, the internal temperature hadrisen to 81° C. At that temperature the internal temperature remainedconstant for several minutes (due to cooling by boiling). Forpost-reaction, the mixture was stirred an additional 1 hr at 80° C., andthen was cooled under stirring.

The dispersion formed was nearly completely free of coagulate. Theparticles obtained were monodisperse, with a mean particle diameter 4.5micron.

The solid was recovered from the dispersion by filtration, or bysedimentation, decanting, and subsequent drying.

EXAMPLE 2

Production of crosslinked polymethacrylate particles with an elevatedindex of refraction:

The following compounds were charged to a 250 mL reactor equipped with acondenser, an N₂ feed, a temperature sensor, a thermostat, and astirrer:

129.55 g cyclohexane

41.16 g methyl methacrylate

27.90 g benzyl methacrylate

0.70 g allyl methacrylate

0.43 g hydrogenated styrene-isoprene block copolymer (SHELLVIS 50®).

The initiator solution comprised 0.70 gbis(4-tert-butylcyclohexyl)-peroxydicarbonate in 6.3 g cyclohexane.

The reactor was purged with nitrogen. The reaction was carried out undernitrogen. The hydrogenated styrene-isoprene block copolymer, themonomers, and the cyclohexane were charged to the reactor. The bath washeated to c. 65° C. After the internal temperature reached 65° C., thereaction was initiated by addition of the initiator solution. After 75min, 0.1 wt. % tert-butyl per-2-ethylhexanoate (based on the weight ofthe monomer mixture) was added, for post-crosslinking. The dispersionwas stirred another 2.5 hr at elevated temperature, and was then cooledand allowed to stand.

The dispersion was free of coagulates. The particles obtained weremonodisperse, with mean particle diameter 7-6.5 micron. FIG. 1 shows theparticles at a magnification of c. 1:1000×.

EXAMPLES 3-12

The procedure was analogous to that of Example 2. The data are reportedin Tables 1 and 2.

Table 1: Dispersion of 99:1 pbw methyl methacrylate-allyl methacrylatecopolymer, with solids content 30 wt. %, usingbis(4-tert-butylcyclohexyl)-peroxydicarbonate as the initiator. (Allpercentage figures in wt. %., based on the weight of the monomermixture.)

    ______________________________________                                                      Hydrogenated                                                    Ex-           styrene-                                                        am-           isoprene block                                                                            Cyclo- Butyl  Particle                              ple  Initiator                                                                              copolymer   hexane acetate                                                                              Size                                  No.  (wt. %)  (wt. %)     (wt. %)                                                                              (wt. %)                                                                              (micron)                              ______________________________________                                        3    0.25     0.63        100    0      3.0                                   4    0.25     0.63        91.4   8.6    4.1                                   5    0.25     0.63        88.4   11.6   4.6                                   6    0.25     0.63        85.9   14.1   4.8                                   7    0.25     0.63        82.9   17.1   5.3                                   8    0.25     0.63        79.9   20.1   6.4                                   ______________________________________                                    

As may be seen, the size of the particles increases with increasingaddition of butyl acetate to the cyclohexane. Comparing Example 11 withExample 4, it is seen that when a hydrophobic monomer is used (isobutylmethacrylate), with an otherwise similar formulation, the particles arelarger. Other possible means of controlling particle size are the solidscontent and the initiator concentration. Increasing both together leadsto larger particles, as may be seen from comparison of Examples 1 and 3.Small amounts of allyl methacrylate do not appear to have a substantialinfluence on the particle size.

Table 2: Dispersion of 90:10 pbw methyl methacrylate-isobutylmethacrylate copolymer, with solids content 30 wt. %, usingbis(4-tert-butylcyclohexyl)-peroxydicarbonate as the initiator. (Allpercentage figures in wt. %., based on the weight of the monomermixture.)

    ______________________________________                                                      Hydrogenated                                                    Ex-           styrene-                                                        am-           isoprene block                                                                            Cyclo- Butyl  Particle                              ple  Initiator                                                                              copolymer   hexane acetate                                                                              Size                                  No.  (wt. %)  (wt. %)     (wt. %)                                                                              (wt. %)                                                                              (micron)                              ______________________________________                                         9   0.25     0.63        96.4   3.6    4.8                                   10   0.25     0.63        92.9   7.1    6.2                                   11   0.25     0.63        91.4   8.6    6.7                                   12   0.25     0.63        89.3   10.7   6-10**                                ______________________________________                                         **Multi-modal                                                            

EXAMPLE 13

Production of crosslinked particles with rough surfaces, comprised ofmethyl methacrylate, phenyl methacrylate, and allyl methacrylate:

In a 500 mL reactor with stirrer, condenser, nitrogen feed, andtemperature sensor, the following mixture was heated to 70° C.:

199 g cyclohexane

68.6 g methyl methacrylate

29.4 g phenyl methacrylate

1 g allyl methacrylate

0.62 g SHELLVIS 50®.

The reactor contents were stirred at 68 rpm. To initiate the reaction, 1g bis(4-tert-butylcyclohexyl)-peroxydicarbonate (as a 10% solution incyclohexane) was added. After c. 2 min, slight clouding was perceptible,and after 10 min the reaction mixture had become white. The internaltemperature was maintained at <74° C. After 75 min the reaction wasterminated. For post-reaction, 0.1 g tert-butyl per-2-ethylhexanoate wasadded, and the mixture was stirred an additional 21/2 hr at 75° C.,followed by cooling. The dispersion was free of coagulates. The particlesize was 8 micron. The particles had a rough surface.

EXAMPLE 14

Production of crosslinked particles with rough surfaces, which particlesare comprised of methyl methacrylate, benzyl methacrylate, and allylmethacrylate:

The following mixture was charged to a reactor as described in Example13, and the mixture was heated to 71° C.:

136.5 g cyclohexane

34.5 g methyl methacrylate

25.1 g benzyl methacrylate

3.1 g allyl methacrylate

0.8 g SHELLVIS®50.

The polymerization was initiated by adding 0.63 gbis(4-tertbutylcyclohexyl)-peroxydicarbonate and 0.06 g tertbutylper-2-ethylhexanoate, in 6.2 g cyclohexane. After 75 min the internaltemperature was increased to 75° C. and stirring was continued for 2 hrat this temperature. A coagulate-free dispersion was obtained. Thedispersion contained <2 wt. % of fines (<1 micron). More than 98 wt. %of the particles had a size of 9 micron. The particles of 9 micron sizewere rough and angular. The particles were filtered out and were driedin vacuum.

EXAMPLE 15

The method differed as follows from that of Example 14: Initiation waswith 0.63 g bis(4-tert-butylcyclohexyl)-peroxydicarbonate dissolved in5.67 g cyclohexane. After-reaction was carried out by addition of 0.06 gt-butyl perneodecanoate in 0.54 g cyclohexane. Stirring was continued anadditional 1 hr at 75° C., followed by cooling and filtration. Polymerbeads with a particle size 8.3 micron were obtained, which were roughand angular. The particles were dried in vacuum.

EXAMPLE 16

Incorporation of the monodisperse particles into polymethyl methacrylatemolding compounds:

6 pbw monodisperse polymer beads according to Example 15 were mixed with94 pbw PMMA granulate (PLEXIGLAS® 8N), and were then homogeneouslydistributed in the melt in a degassing extruder at 230° C. The resultingextruded strings were granulated.

EXAMPLE 17

Meter covers were injection molded from the granulate according toExample 16. The meter covers had high transparency and optimaldispersion.

Sample thickness: 2 mm.

Energy half-value angle (gamma/2): 15°.

Transmissivity, T: 90%.

EXAMPLE 18

Incorporation of the monodisperse particles into high impact PMMAmolding compounds:

6 pbw monodisperse polymer beads according to Example 15 were mixed with94 pbw PLEXIGLAS® zK6A, and the mixture was granulated.

EXAMPLE 19

The granulate according to Example 18 was applied in a 100 micron layerthickness to 3 mm ABS (as a support), in a coextrusion process. Thecoextrusion composite was distinguished by a satin finish.

Roughness (measured with a Perth-O-Meter):

RA=0.38

RZ=2.60

Rmax=3.02.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

This appplication claims the benefit of priority under 35 USC 119 toGerman Patent Application P 43 27 464.1. filed in the German PatentOffice on Aug. 16, 1993, the entire contents of which are herebyincorperated by reference.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:
 1. Monodisperse particles of poly(meth)acrylatescomprising units of the monomersi) methyl methacrylate; ii) phenylmethacrylate; and iii) a graft crosslinking agentwherein said particlehave diameters in the range 4-12 micron.
 2. Monodisperse particles ofpoly(meth)acrylates comprising units of the monomersi) methylmethacrylate; ii) an aralkyl methacrylate selected from the groupconsisting of benzyl methacrylate, phenylethyl methacrylate, andphenylpropyl methacrylate; and iii) a crosslinking agent;wherein saidparticle have diameters in the range 4-12 micron.
 3. The monodisperseparticles of poly(meth)acrylates of claim 2 comprisingi)methylmethacrylate; ii) benzyl methacrylate; and iii) a crosslinkingagent comprising allyl methacrylate.
 4. Monodisperse particles ofpolymethacrylates comprising units of the monomersi) methylmethacrylate; ii) benzyl methacrylate; and iii) a crosslinking agentcomprising allyl methacrylatewherein said particles have a roughsurface, and a particle diameter in the range 7.5±2 micron.
 5. Themonodisperse particles of polymethacrylates according to any one ofclaims 1-3 wherein said particles are a particle size range 5-11 micron,wherein said particles have rough surfaces.
 6. A paint comprising0.01-30 wt. % of the monodisperse particles according to any one ofclaims 1-4.